Nature-Based Solutions Show Superior Urban Cooling and Carbon Savings in Busan

A groundbreaking study by researchers at the Department of Ecological Engineering, Pukyong National University in South Korea, has shed new light on how cities can confront rising urban heat, ballooning energy demands, and the urgent need for carbon neutrality. Published in Geography and Sustainability (2025), the paper by Jinwook Chung and Kijune Sung examines how a range of nature-based solutions (NbS), from green and cool roofs to roadside greenery, urban parks, and restored forests, can alter the climate resilience of urban areas. Using Busan, Korea’s bustling coastal metropolis, as the case study, the research looked not only at cooling effects but also energy savings, carbon sequestration, and the broader economic outcomes of different interventions. The results carry lessons that extend far beyond Korea’s borders, offering a science-backed roadmap for cities worldwide.

A City Under Pressure

Urbanization is accelerating at an unprecedented pace. By 2050, nearly 70 percent of the global population will reside in cities, according to United Nations estimates. The consequences are already evident in rapidly growing cities like Busan, which has witnessed a 53 percent expansion of its urban area since 2000. This expansion has replaced green landscapes with asphalt, concrete, and dense high-rises, amplifying the urban heat island effect, where urban centers become significantly warmer than their rural surroundings. In Busan, average temperatures have risen by more than a degree Celsius in the past half-century, intensifying summer heatwaves and escalating demand for air conditioning. These changes create a vicious cycle of energy consumption and carbon emissions, which in turn exacerbate climate change. Against this backdrop, NbS are increasingly being considered as not just cooling measures, but as essential strategies for sustainable and climate-resilient urban planning.

Testing Nature Against Concrete

To explore the impacts of NbS, the study deployed the InVEST Urban Cooling Model (UCM), a tool capable of simulating how different land-use changes affect heat mitigation, energy consumption, and carbon flows. The scenarios considered included building-level adaptations such as green roofs and reflective cool roofs; land-use adaptations, including new parks, roadside green space expansion, and forest restoration; and combination strategies that layered multiple interventions simultaneously. The researchers even modeled a worst-case scenario of continued deforestation to compare the costs of green space loss.

The results revealed sharp differences. Cool roofs proved more effective than green roofs in directly reducing air temperature, lowering citywide averages by 0.26°C compared with 0.17°C for green roofs. Yet cool roofs could not sequester carbon, unlike vegetated surfaces. Among land-based solutions, urban parks stood out as the most powerful single measure, capable of lowering air temperature by up to 0.72°C. Roadside greenery delivered both cooling and carbon benefits, while forest restoration offered the strongest combined performance in terms of energy savings and carbon sequestration. Most compellingly, combination measures, integrating cool roofs, urban parks, roadside greenery, and restored forests, produced the most significant reductions, lowering Busan’s average temperature by more than half a degree and achieving localized cooling of up to 1.6°C.

Counting Energy, Carbon, and Cash

The climate benefits are translated directly into energy savings and carbon reductions. Full-scale green roofs reduced energy use by just over 3 percent, while cool roofs achieved a 5.5 percent reduction. Urban parks, however, saved more than twice as much energy as either roof-based option, while roadside green space expansion and forest restoration provided impressive gains, especially when adjusted for their smaller application areas. Forest restoration was nearly three times more effective than cool roofs when area efficiency was considered, while deforestation triggered the opposite effect, raising temperatures and wiping out more carbon storage than cool roofs could compensate for.

Financially, the numbers are striking. Restoring forests generated nearly $20 million worth of carbon sequestration benefits. Combination strategies delivered the largest total economic returns, combining reductions in energy bills with lower emissions. Urban parks, when considered relative to their footprint, saved more money than any other measure, nearly five times more than green roofs and more than twice as much as combination measures. Conversely, continued deforestation caused staggering losses, over $21 million in lost carbon value and millions more in increased cooling costs.

Designing Smarter Green Cities

Beyond the numbers, the study underscores the importance of design, location, and plant choice. While cool roofs were stronger than green roofs for cooling, vegetation provided multiple ecosystem services, stormwater control, air quality improvement, noise reduction, biodiversity, and long-term carbon sequestration. For urban parks, location mattered: scattered small parks at city edges produced wider cooling effects than single, large central parks. Plant selection also played a decisive role. Broadleaf trees such as maples cooled more effectively than conifers, while mixed plantings balanced biodiversity and carbon storage with shade and cooling. These details highlight the need for cities to adapt strategies to their specific landscapes, rather than adopting one-size-fits-all solutions.

The researchers stress that preserving existing forests should be a first priority. Mature forests provide unmatched carbon storage, biodiversity, and cooling, benefits that cannot be replicated by constructing new parks or planting rooftop gardens. Once lost, these services are nearly impossible to replace.

A Blueprint for Carbon-Neutral Cities

The overarching conclusion is clear: no single measure can fully mitigate the urban heat island effect or push cities toward carbon neutrality. Instead, multi-pronged strategies tailored to local land use hold the greatest promise. Dense urban cores may benefit most from rooftop adaptations and strategically placed parks, while suburban and peri-urban zones should focus on restoring and preserving forests. In all cases, combining approaches delivers the greatest overall benefits.

The study by Pukyong National University provides compelling evidence that cities must look to nature as a key ally in confronting climate change. NbS are not only cooling strategies but also energy savers, carbon sinks, and financial assets. Urban planners and policymakers now have a clearer picture of how natural infrastructure can complement built infrastructure, offering a sustainable pathway to livable, resilient, and carbon-neutral cities. The message is unmistakable: cities cannot concrete their way out of the climate crisis; they must integrate and protect nature at every scale, from rooftops and roadsides to parks and forests.